Abstract

When planning for closure, mining operations need to consider that closure timeframes can be more than 100 years. Cover systems designed to support a returning land use plan are subject to changes in climate far into the future. Effective and safe management of climate risk requires a deliberate approach to understanding, assessing, and responding to the potential impacts of climate change at a site-specific level. It is critical that climate change risk be appropriately quantified and incorporated into closure plans and cover systems designs to resiliency and capacity for adaptation over the long-term. 

Boliden is in the process of updating its closure plan for the Aitik Mine site (Aitik) in northern Sweden. A major component of the workflow involves incorporation of a risk-based approach to support closure planning; specifically, using the Failure Modes and Effects Analysis (FMEA) approach to inform on design. A primary feature being evaluated is the engineered cover systems for the waste rock storage facility and tailings management facilities. The primary objectives of the closure cover systems are to manage oxygen ingress to the underlying waste materials, manage net percolation of meteoric waters, and to provide a medium for development of a vegetative cover consistent with return land use objectives.

A site-wide loading and water balance informed the decision-making process within the FMEA framework. Boliden’s Project Team evaluated metals and acidity loading from the discrete mine domains under operations and closure conditions in order to predict impacts to the downstream receiving waterbodies.  For each of the loading assessments, inputs to the water balance were driven by a common synthetic climate data set developed by The Swedish Meteorological and Hydrologic Institute. An important failure mode identified as part of the FMEA process was that the range of climatic conditions encountered may not be represented by the climate datasets used in the loading simulations. Therefore, Okane completed cover system sensitivity analyses by modelling the driest and warmest of the available climate datasets to maximize the range of climate conditions examined. Evaluating the cover system alternatives in this context provided rationale to adopt a cover system incorporating a bentonitic lower permeability layer. This approach will provide an increased probability of meeting performance objectives in a wider range of climatic conditions.  Outcomes of Okane’s assessment have highlighted the importance of considering potential implications of climate change in cover system design, even while an existing compacted till cover system design has performed well in monitored field trials under current conditions.